Scientists test tale of 'crow and pitcher'

RESEARCH

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Aug 17 2009, 17:54 ist

updated: Aug 17 2009, 17:54 ist

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esop’s fables have ageless values to teach children about the basics of life. But at least one such tale has now been found to be scientifically correct as well. Aesop used the ‘crow and the pitcher’ story to explain that “necessity is the mother of invention”. It is about a thirsty crow using pebbles to raise the level of water in a pitcher to quench its thirst.

Rooks do the same

British scientists have now demonstrated that rooks – a cousin of the crow – do exactly the same.

Four rooks drop pebbles in a plastic test tube to increase the level of water on which a worm is floating. The bug is the prize catch for the birds who know exactly how to use stones to increase water levels.

In the first part of the study, researchers varied the height of water in the test tube so that the rooks used stones to raise the water level to reach a bug floating on top. The clever birds were very adept and highly successful regardless of the starting level of the water and the number of the stones needed.

Rooks belonging to the corvid (crow) family were used in the experiment.

Two of the birds were successful on their first attempt to raise the height of the water to a level at which the worm floating on top could be reached whereas the other two birds needed a second try.

The birds were highly accurate in their ability, adding the exact number of stones needed to raise the water level to the necessary height.

Additionally, rather than attempting to reach the worm after dropping each stone, they estimated the number needed from the outset and waited until the appropriate water level was reached before dipping their beaks into the tube.

In the second experiment, the rooks were presented with stones which varied in size. The rooks after a few attempts selected larger stones over smaller ones for dropping into the water.

The birds learnt rapidly that larger stones displaced more water and they were able to obtain the reward more quickly if they used bigger stones rather than the small ones.

Ability to distinguish

From the third experiment, the scientists inferred the rooks were able to distinguish between sawdust and water.

They recognised sawdust could not be manipulated in the same manner as water and therefore when presented with the choice between a tube half-filled with either sawdust or water, rooks dropped the pebbles into the tube containing water and not the sawdust.

“This is remarkable considering their brain is so different from the great apes. Although it has been speculated in folklore, empirical tests are needed to examine the extent of their intelligence and how they solve problems,” said Christopher Bird at the University of Cambridge who is the principal investigator. The findings were published in the August 6 issue of the journal Current Biology.

“Corvids are remarkably intelligent, and in many ways rival the great apes in their physical intelligence and ability to solve problems. The only other animal known to complete a similar task is the orangutan,” Bird said.

Although the study demonstrates the flexible nature of tool use in rooks, they are not believed to use tools in the wild.

“Wild tool use appears to be dependent on motivation. Rooks do not use tools in the wild because they do not need to, not because they can’t. They have access to other food that can be acquired without using tools,” he said.

In an accompanying commentary in the journal, Alex Taylor and Russell Gray of the University of Auckland in New Zealand mentioned an earlier experiment in which the rooks had dropped a single stone into a tube to get food released at the bottom.

Is it possible that maybe the birds were just following that strategy again when they saw the tube in the new experiment?

Cambridge scientists argued otherwise. Bird said rooks dropped multiple stones rather than just one before reaching for the worm and they reached for it at the top of the tube rather than checking the bottom.

Was Aesop’s crow a rook?

Aesop’s crow might have actually been a rook, since both kinds were called crows in the past. And their skills in using tools can easily make every one of them Einsteins of the crow family.

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